1. Field of the Invention
The present invention relates to a surveillance signal apparatus, particularly a signal lamp, a signal key, a signal switch or the like with a case having electrical terminals and with an apparatus head disengagebly attached to a the casing, where the apparatus head contains signal part supplied with electrical power.
2. Brief Description of the Background of the Invention Including Prior Art
It is a disadvantage with known surveillance signal apparatus of this kind that in use in spaces which are in danger of explosions or the like corresponding pressure sustaining encapsulations are also to be provided for the apparatus head. The mounting at the front plate of a switching cabinet or other provisions can only be performed with special tools in order to prevent an unintended disengagement in the endangered space area.